Almost all public buildings are required to have signs identifying emergency exits. These signs are generally rectangles and are perhaps twelve inches long and eight inches high. The dimensions may vary depending on the code or standard governing the size of the signs.
Most of these signs are illuminated by incandescent lamps. In order to illuminate the entire sign, two twenty-watt lamps are usually required. Most fire codes require that the signs be lit continuously while the building is occupied. Since many public buildings have numerous exits, a single building may have hundreds of signs, consuming thousands of kilowatts of electricity per year. In addition, the signs generate heat which must be removed during the air conditioning season. Since the signs are located near ceilings, the heat input during the heating season is minimized because much of the heat is conducted and convected along the floors to the exterior walls of the building. Moreover, at least one of the emergency exit light bulbs can be expected to burn out during the course of the year. When a building has hundreds of emergency exit signs, the cost of replacing these bulbs can be quite high. It has been estimated that each emergency exit sign costs between $70 and $120 per year to operate and maintain.
The electro-luminescent emergency exit sign disclosed in U.S. patent application Ser. No. 353,390 may have the disadvantage of not appearing to be on or lit if background lighting is at a certain level. In other words, the regular lighting in the room or hallway containing the emergency exit sign may appear brighter than the light emitted by the emergency exit sign itself. Consequently, the fact that the sign is energized may not be apparent to an observer, even though once the background lighting is extinguished or substantially diminished, the electro-luminescent sign appears lit. Fire inspectors are used to seeing emergency exit signs in which incandescent bulbs emit illumination from a small area which illumination is bright enough to be seen above the ambient or regular room illumination. When the fire inspector does not see light being emitted from the sign, he assumes that the sign is out and that it will not be visible in the dark. Accordingly, if the concept set forth in U.S. patent application Ser. No. 353,390 is to be acceptable to many fire inspectors, the fire inspectors need an indication that the exit signs utilizing electro-luminescent lamps are energized so that they will be visible in the dark. This is especially the case with exit signs utilizing electro-luminescent panels having extremely low wattages. For example, this is a problem with the electro-luminescent panels manufactured by the Potter Electronics Company of Charlotte, N. C., which successfully illuminate emergency exit signs in darkened rooms with a power consumption of less than one watt.
The light output of electro-luminescent lamps tends to degrade with time. After years of service, a lamp may become so dim that the sign it lights is not readily visible in a darkened room. Consequently, there is a need for a monitor which informs maintenance people that the lamp needs replacement or servicing. With emergency exit signs using incandescent lamps, it is readily apparent that a lamp is on or off simply because one can readily see if a twenty-five watt incandescent lamp is either lit or unlit above regular or ambient lighting.
If emergency exit signs utilizing the principles set forth in U.S. patent application Ser. No. 353,390 are to be widely adopted, it is necessary that such signs be configured for convenient retrofitting to existing exit sign housings so as to minimize the difficulties for those who wish to take advantage of the energy and maintenance savings inherent in such signs.